Method for coating and infiltrating a porous refractory body



Jan. 26, 1960 s. E. TARKAN ET AL 2,922,721

METHOD FOR COATING AND INFILTRATING A POROUS REFRACTORY BODY Filed April2, 1956 2 Sheets-Sheet 1 FIG. IE.

FIG. IB.

and $2110.? 6. 6057251.

FIG. IA.

Jan. 26, 1960 s. E. TARKAN ET AL 2,922,721

METHOD FOR COATING AND INFILTRATING A POROUS REFRACTORY BODY Filed April2, 1956 2 Sheets-Sheet 2 .5 IQF'ACE R p 6 a 7 x i 5 5 i 7x A 1! Y {a jCOAT/N6 I N V EN TORS 572/44? TE. 72.?K/IV, #5440!!! Z Ih EWQ METHOD FORCOATING AND INFIL'IRATING A POROUS REFRACTORY BODY Stuart E. Tarkan andHenry W. Lawendel, New York,

and Claus G. Goetzel, Yonkers, N.Y., assignors to Sintercast Corporationof America, Yonkers, N.Y., a corporation of New York Application April2, 1956, Serial No. 576,230 11 Claims. (21. 117-55 The presentinvention.- relates to coated refractory metal compound composites, andmore particularly to a method for obtaining adherent metal coatings uponrefractory metal carbide materials characterized by improvedmetallurgical'quality, improved resistance to oxidation, improvedresistance to thermal and mechanical impact or shock, and generallyimproved properties at elevated temperatures.

The advent of modern jet engines, rockets and other types of primemovers involving heat engines operating at elevated temperatures ofup toabout 1000 C. and higher has provoked intensive research in thedevelopment of high temperature materials, particularly in thedevelopment of thermal elements, for example fluid guiding elements suchas turbine blades, buckets, nozzles, vanes, guides, partitions, etc.,which inuse are exposed to corrosive gaseous atmospheres. The use ofspecial fuels containing lead compounds, vanadium compounds and othercompounds either present as additives or inherent in the fuelcomposition have been particularly troublesome in view of harmful vaporsof lead oxide, vanadium pentoxide, etc. which are given off duringcombustion of the fuel and which readily chemically attack and corrodeunprotected component parts of heat engines at elevated temperatures.

In an attempt to solve the foregoing problem, certain wrought and castheat resistant alloys of special corrosion resistant compositions were.developed. However, these alloys were limited in their applicationbecause of their melting points which range in the neighborhood of about1300 C. to 1500 C. As more powerful jet engines were designed to operateat higher temperatures, additional burdens were placed on these alloyswhich had to be replaced by more stable materials of higher meltingpoint.

An outstanding material which was developed and proposed to meet thisneed was a refractory carbide material consisting of about equalproportions by weight of titaniurn carbide and an alloy of the so-calledsuper alloy type usually containing nickel or cobalt as major alloyingconstituents, and chromium, tungsten, molybdenum, titanium, iron,aluminum, etc. as other alloying constituents. This material couldeither be prepared by the well-known cementing method employed in thepowder metallurgical production of carbide tools, that is by mixingrefractory carbide particles with a given amount of binder metal, forexample nickel or cobalt or an alloy based on these metals, followed bypressing the mixture into a desired shape and thereafter sintering it;or the material could be produced by forming a sintered porous skeletoncomprising a refractorymetal carbide and thereafter infiltrating it witha heat resistant metal or alloy to form a strong composite structure.The latter method was preferred over the former as it enabled theconsistent production of superior materials. It was found that thermalelements produced by infiltration comprising about 50% by Weight oftitanium carbide and about 50% by weight of a nickel base alloycontaining about 13% 2,922,721 Patented Jan. 26, 1960 to 15% chromiumand about 6% to 7% iron as alloying constituents could withstand astress of about 42,000 p.s.i. at a temperature of about 875 C. for 100hours in an oxidizing atmosphere before it would rupture. Itwas, alsofound that the same material at 985 C. would withstand a stress of16,000 psi. before it would rupture after 100 hours of testing. At thelower temperature, the thermal elements after testing exhibited anelongation of the order of about 2% to 3% and an impact strength ofabout 10 ft. lbs. for a Charpy-type unnotched bar, while at the highertemperature they exhibited an elongation of about 4% to 8% and an impactstrength of about 6.5 ft. lbs.

The foregoing properties have been found satisfactory for parts to beused in short time applications in jet engines, and performance recordsof up to about 100 hours have been established in actual service tests.However, present demands for increasedservice life under more aggravatedservice conditions prevailing in the latest jet engine and rocketdesigns have necessitated the development of even better hightemperature materials. It was found that it was necessary to improveoxidation resistance, strength, thermal shock and impact resistance ofrefractory metal carbide composition at temperatures in the rangebetween 950 C. and 1050 C. and bring these properties in closer accordwith the extremely good properties which were established for these samematerials at 875 C. v

It was observed that while these materials were a substantialimprovement over Wrought or cast heat resistant alloys, they tended tofail during prolonged service as a result of surface deterioration dueto oxidation and cor-' rosion at temperatures above 900 C. and of theorder of about 950 C. to 1050 C. It was found that surface,deterioration would occur due to corrosion which markedly deleteriouslyaffected the impact resistance and strength of the material. The failurewas usually of a type characteristic of brittle materials. It was feltthat, in order to inhibit such surface attacks and sustain theproperties of the material, it would be necessary to'provide aprotective surface coating around the exposed working surfaces of themetal carbide composite was to protect it from hot corrosiveatmospheres. Various, methods have been proposed for providing suchprotective coatings to refractory'compound composites. Thus, accordingto US. Patent No. 2,714,245, granted to Claus G. Goetzel on August 2,1955, and assigned to the present assignee, the protective coating couldbe achieved during infiltration, of a porous skeleton body by firstproducingthe porous body (.e.g. a turbine blade) slightly undersized,centering it in the cavity of a mold comprising a substantially inertrefractory, the cavity conforming in shape to but being slightly largerthan the body, infiltrating the body and allowing for suificient excessinfiltrant to fill the space between the blade and the mold walls toprovide for the coating. Coatings of controlled thickness produced inthis manner markedly improve the properties of turbine buckets,providing extreme care was taken in indexing the skeleton in the moldcavity to insure obtaining the desired coating dimensions and alsoprovided the heating cycle was carefully controlled to minimizenon-uniformshrinkage or warpage of the inert refractory. Also care hadto be taken to control the infiltration process so that theinfiltrant'metal during infiltration did not gush down the sides of theskeleton and erode its surface.

In copending application U.S. Serial No. 485,568, filed January 28,1955, in the names of Claus G. Goetzel,

Nicholas J. Grant, Leonard P. Skolnick and Jack A.-

Yoblen, and assigned to the present assignee, a method for coatingrefractory metal compound composites is disbonded, relatively ductilecoating by controlling the relative temperatures of the composite andthe cbatingma:

teriall so as to'preverit embrittle'rnent of the coating by excessivediffusion of the base material into it. Improved results could beconsistently obtained by this; concept provrdedzthe necessary care was'taken to control the relative temperatures of the materials to bejoined.

. The present invention differs over the'foregoing concepts m that anentirely new approach is utilized for coating metal compound compositesproduced by infiltratron. It is particularly applicable to theproduction of coated products having a tapered configuration, forexample, fluid guiding members, such as turbine buckets or nozzle.vanes, characterized by a thick portion near the lead ng edge taperingsmoothly and arcuately to a relatively thin trailing edge portion.Generally speaking, tapered bodies area little more ditficult to coatsubstantially uniformly, particularly when the coating is carried outsimultaneously with infiltration in amold. Even whenihe skeletonfluid-memberis'properly indexed in a mold 'with'a space provided between.the'skeleton and the mold for receiving the infiltrant metal coating,movement of the body withinjhe'mold or movement of the mold wallsthemselves during heating isapt' to throw off the indexed skeletonsufliciently to effect deleteriou sly the uniformity of the coating. V

An improved method has now been discovered whereby ,the foregoingdisadvantages are .greatly minimized wherein the skeleton body prior toinfiltration is produced as a composite structure which obviatesthenecessity of accurately indexing the skeleton in the moldwhen'producing a coated body by infiltration.

Another important advantage is that the improved method also minimizeserosion of the skeleton surface during the combined infiltration and.coating step. It is the object of the invention to provide a combinedinfiltration and coating process for producing coated infiltratedcomposites comprising a high melting point re fractory metal compoundmaterial, for example titanium carbide. I

Another object is to provide a method for producing a coating ofimproved metallurgical quality on infiltrated refractorymetal compoundmaterials.

, These and other objects will more clearly' appear when taken inconjunction with the accompanying drawing wherein:

Figs. 1A to 1F depict inflow sheet arrangement the steps and materialswhich may be employed in carrying out an embodiment of the invention;

Fig. 2 illustrates an expanded view of the boundary conditions whichprevail in an embodiment of the invention between the mold and theskeleton prior to in filtration in the production of a coated body;

Fig. 3 is. similar-to Fig. 2 but shows the penetration of the infiltrantmetal into the interstices of the skeleton and the" primary coating byinfiltration; and

Flg. 4 is a representation of a photomicrograph at 250' magnificationofa transverse section of the final productv showing a relatively sharpline of demarcation between the coating and the base material.

In carrying the invention into practice, the porous skeleton body to beinfiltrated is provided with a foundation layer or primary coating of ametal alloyable with the infiltrant metal, the thickness of theprimarymetal coating determining to a large extent thedesired thicknessof the final coating. Once the skeleton body is prm vided with theprimary coating, it need only be inserted in -a powder pack ofsubstantially inert refractory, e.g. thoria, zirconia, beryllia,alumina, etc, without taking the usual precautions of indexing the bodyto insure a' coating of accurate dimensions. In other 'words, the

primary coating of the composite skeleton also serves mold comprises theporous skeleton on one side, a primary metal coating of desiredthickness on the surface thereof and on the other side of the primarycoating a back-up support of substantially inert refractory oxidematerial. The composite skeleton is subjected to infiltration in theusual manner with a matrixforming metal which flows through the skeletonfilling u'p'the pores and on out through the surface thereof merging andal-' loying with the primary coating. The flowing of the molteninfiltrant metal but of the skeleton surface and into the primarycoating is referred to as exfiltration and the use of this andequivalent expressions hereinafter is meant to cover the aforementionedphenomenon.

The primary coating metal employed in carrying out the invention shouldbe one which will combine with the infiltrant to form a coating havingthe desired properties, i.e. having resistance to corrosion, erosion andoxidation and adequate ductility, hardness, etc. The metal should have amelting point higher than the melting point of the matrix-forminginfiltrant metal so that the foundation layer provided by theprimarycoating will not be prematurely disrupted before completion ofthe exfiltration step. Thus it is preferred that the melting point ofthe coating metal should be atleast 50 degrees higher than the meltingpoint of the infiltrant metal in the pores of the skeleton.Additionally,,the. primary metal coat should not combine with thematerial of the skeleton to form a liquid phase at a temperature belowthe melting point of the matrix-forming infiltrant metal.

Goodresults are obtained by applying the metal coating in particulateform, powdered metal being preferably employed as the primary coatingmetal, although the coating metal may be applied by wire spraying, metalplating, etc; V

In building up a primary coating on a skeleton surface from powderedmetal, a suspension of the metal in a liquid containing a fugitivebinder has been found very satisfactory. The concentration of metalpowder in the liquid binder may range from 1' to 3 grams per cubiccentimeter of binder solution. The coating may be applied by painting,spraying or dipping, which after drying forms a hard layer capable ofwithstanding the usual amounts of shock which prevail during handling,etc. The dried coating can be shaped to the desired thickness, makingallowances for volume changes during treatment, and the coated skeletoninserted into an investment pack for heating to remove the fugitivebinder and to sinter to some degree the metal powder to form in thiscase a porous primary coating into which the infiltrant metal flows byexfilt'ration from the skeleton during the subsequent infiltrationprocess. Since the infiltrant phase is substantially common to both theskeleton body and the finally produced coating, a dense metallurgical'bond is assured. a t Nickel has been found very satisfactory as theprimary coating material. Finely divided nickel powder, preferably'finer than 140 mesh size (U.S. standard), suspended in a liquid varnishor resin binder, has proven particularly successful as a primary coatformer. When employing metal powders generally as the primary coat,substantially all of the powder should preferably range in size fromabout minus to plus 325 mesh. After thecoating is formed on a skeletonbody by painting, dipping or spraying, and the resin cured by heating toan elevated 'curing temperature, the coated body is then subjected to aninfiltration cycle during which the binder is volatilized and drivenoff. 'If the resin has a high vapor pressuredeleterious to theinfiltrationfcycle, the volatilizationis then eflected prior toinfiltration under substantially inert conditions while the compositeskeletonisiembedded in the refractory ,powder pack.

If-desired, the nickel primary coat maybe produced by spraying using ametallizing gun and nickel wire as the material source, I re insuresomeadherence of the coating. to the skeleton, the surface of theskeleton is treated with a phenolic resin solution of medium viscosity(e.g. phenol formaldehyde) the excessLofwhichis wiped ofiand thematerial remaining on the surface and in the surface pores then cured ata temperature of about 350 F. The surface is lightly sand-blasted andthen followed by spraying of the nickel to produce a primary coatingwhich adheres to the resin treated surface As I before the resin isremoved by volatilization either durplied a primary coating comprisingbonded nickel powder shown in Fig. 1D. The skeleton with primary coatisv inserted in a refractory oxide powder pack in the mold shown in Fig1E as comprising in cross section a graphite flask} against which issupported powder pack 3 which in 'turn supports the composite skeletoncomprising ti- 'tanium carbide with primary nickel coat 1. Thetop. rootportion 4 of the blade skeleton is left uncoated and has applied to itinfiltrant metal 5 plus sufficient excess ready for infiltration intothe pores of the skeleton and exfiltration from' the surface of theskeleton into the primary coating to form the final dense coating 6shown in Fig. 1F.

he: bo nda y nd t ons te a l bet n t e @91 1 surface, the primarycoating, and the skeleton, is illustrated by the expandedcross-sectional representation of Fig. 2 which shows the flask portion2a, a packing of refractory oxide 3;; adjacent it supporting thecomposite skeleton comprising a porous foundation layer of nickelprimary coating 1;: adhering to'the" porous skeleton portion 7 oftitanium carbide. Fig. 3 is the same as Fig. 2 except that it shows theinfiltration metal 8 in skeleton body 7. and also in primary coat 1cafter exfiltration from the skeleton into the voids of the primarycoatingat the instantbefore the, infiltrant has completely combined andalloyed with the material of the primary coating.

It will be appreciated that at this point of. the infiltration aconcentration gradient will exist in the infiltrant, the infiltrant 8surrounding the titanium carbide particles 7 being slightly enriched intitanium carbide due to the rounding ofi of the particles, and theinfiltrant surround ing the partially dissolved primary coat 1a beingenriched in ni kel- Qt Q set e i filt n i hqm enized te u the s a ns sulin n. ompl l ion ft e.

primary co a sho n, Fi

Fi 4 whic s a n escm ti 9 a nhq omi m rap is theactual appearance of theboundary conditions after. complete infiltration and exiiltration hasoccurred with complete alloying of thefinfiltrantwith thecoating reuit abs a ti y o o ene m t x s u tur on ainin me p ecip tated t tan mrarb deown.

by a transversesection through the base surface and the finally producedcoating. the relatively sharp line of demarcation resulting from thismethod of coating thus showing that the originalv surface vof.thecarbide is not disrupted to any significant degree.

As illustrative of the invention, thefollowing examples aregiven;

' Example 1 A-suspens oa o 2 r ins f, a b nyl c e p wde of 400 meshsize. (U.S.. standard). in cubic centi meters of a cementing solutioncomprising a natural resin dissolved in a chlorinated solvent (of thetype sold The figure also illustrates-.

by the Wall Colmonoy Company under the trademark Nicrobraz is employedin producing a primary coating on a sintered porous body of titaniumcarbide (60% dense) of approximately 0.2 inch square and 2 inches long.A layer of about 0.01 inch of the nickel was applied to the surface ofthe bar leaving one end face of the bar uncoated for receiving theinfiltrant metal. After the coating hardened the resulting compositeskeleton was packed in a ceramic powder pack, e.g. thoria, in the mannershown in Fig. 1E. A given amount of a heat-resistant nickel-baseinfiltrant alloy including an excess for exfiltration purposes (aboutnickel to 20% chromium), was placed on top of the uncoated end face ofthe, skeleton and the whole subjected to infiltration at above themelting point of the alloy but below the melting point ofthe nickelprimary coating. The alloy had a melting point of slightly more than 50C. below that of nickel. The infiltration was carriedout at asubatmospheric pressure of about 5 microns in an induction furnace tothe point of completion of exfiltration. Photomicrographs of a mountedsection similar to Fig. 4 indicated that the interface between the bodyand the coating was entirely sound and that substantially no deformationof the original skeleton occurred, that is a relatively sharp boundaryline between the carbide base material and the coating was maintained, vImpact resistance of the coated specimen ranged from 7. to 9 inch-poundsbased on an Izod drop impact test on a 3/ inch square cross sectionspecimen.

, Examp A titaniumcarbide. skeleton body (about 60% dense) was producedmeasuring 0.17 by 0.17 inch square and approximately 2 inches long.20-grams of relatively coarse nickel powderall passing through a mesh(U.S. standard) screen but remaining on a 325 'mesh screen suspended in10' cubic centimeters of cementing solution comprising a; natural resindissolved in a chlorinated solvent defined in Examplel was employed inproducing the nickel coating. The coating thickness was about 0.03 inchover the surface of the bar with the exception of one end face which wasused as the infiltrant contact face. After, the coating was. allowed toharden, the coated-skeleton. was packed in thoria powder with theuncoated end faceleft exposed to which was applied a heat-resistingnickel-base alloy comprising by weight about 13% to 16% chromium, about6% to 8% iron, about 0.4 to 0.8 aluminum, about. 2.25 to 2.65% titanium,about 0.2 to 1.2% columbium, up to about 0.1% carbon, and thebalancesubstantially nickel. The assembly was heated slowly at asubatmosphe'ric pressure of about 10 microns in an induction furnace totheinfiltration temperature during which time the residual binder in theprimary coat was driven off leaving behind a partially sintered primarycoat of nickel powder illustrated in i Fig. 2. The final infiltrationtemperature .was'above the infiltrantmelting point of about 14lQ C. butbelow the meltingpointof the nickel primary coat. The temperature washeld for about 20 minutes at and near the 'mel ting point. The moltenin'filtrant spread through the interconnectingpores of the skeleton byvirtue of the capillary action thereof assisted by the force of gravity.The excess infiltrant exfiltrated from the surface of the carbideskeleton into the overlying primary coating and merged with it to form adense coating of uniform alloy composition. Like Example 1, thephotornicrograph showed a structure similar to that illustrated in Fig.4, that is it revealed a substantially sharp boundary line between thecarbide base material and the dense alloy coating.

Example 3 The procedure asoutline'd in Example 2 was followed exceptthat another-type binding solution was employed informing thenickel'slurry. yThe 20 grams ofnickel powder was suspended in a solutionofcthyl; cellulose 1. await and acetone (solution prepared by dissolvingone gram of ethyl cellulose in 10 cubic centimeters of acetone) andreach the temperature, at which temperature it was'held for anadditional hour to insure'freeing the primary coat-- ing of the ethylcellulose binder and to effect at least a partial sintering of thenickel powder. The coated skeleton was then furnace cooled underhydrogen to room temperature after which it was subjected toinfiltration in accordance with the steps of Example 2. Y

Example. 4

A skeleton titanium carbide body, the same as that described in-Example2, was coated with a 0.02 inch nickel layer by dipping the skeleton in'amedium viscosity phenolic resin' (heat setting type, ephenol-formaldehyde) and the excess wiped olf. The top face was leftuncoated to provide contact with the infiltrant. The dipped skeleton wascured for 20 minutes atabout 250 F. (177 C.) to harden the coating. Thebody was'cooled and then sand blasted at about 25 pounds per square inchair pressure using 60'mesh al uminu'm' oxide abrasive and then followedby spraying using'a Brown and Sharpe gauge nickel wire and a Metco 4Egun manufactured by the Metallizing Engineering Company, the bar beingrotated in a lathe during spraying. Ihe spraying was started at adistance of 15 to 18 inches, and after'acontinuous coat was applied, thenozzle of the "gun was brought to within 10 inches of the specimenfor'the balance of the spraying.

The coated body wasthen infiltrated-as described in- ExampleZ withthe-nickel-base alloy defined in said example. The microstructure of thefinal product was as sound as that illustrated by the photomicrograph ofFig. 4.

The impact strength of the bar, after grinding down to 0.19 by 0.19 inchsquare cross section (i.e. to a coating thickness of about 0.01 inch),was about 7.5 inch-pounds at room temperature and about 10 inch-poundsat1800 F. (about 982 C.). The bar exhibited .thesame impact value evenafter heating for 2-4 hours in still air at Example 5 In producing anairfoil-like shape having approximate dimensions of about 4 inches long,2'inches wide, and a employed. Thus, in. preparinga primary coat ofabout 0.01 inch on all airfoil surfaces, the same suspension of nickelpowder in the cementing solution is used, an end face of the airfoilbeing left uncoated to receive infiltrant metal-Q Thereafter, theprepared airfoil section'is infiltrated in the same manner as the methoddescribed in Example 2. p v

'As has been indicated hereinbefore, the method of the invention asdescribed in Examples 1 to 2, and in particular in Example 5, isespecially adapted to the coating of tapered bodiesysuch'as turbinebuckets, diaphragm nozzles and varies, and other fluid guiding memberscharacteri'zed 'by a relatively thick section tapering smoothly and'arcuately into relatively thin edges. In utilizing the foregoingmethods in the production'of a' turbine bucket, the steps outlined inthe flow sheet of Figs. 1A to IP would be employed.

'Besides nickel, other metals may be employed in producing aprimarycoating, provided these metals are compatible with the infiltrantr'netalarid alloy with it in pro.- ducing the desired coatingij suchother metals may include cobalt, iroin. chromium, tungsten, molybdenum,

tantalum, ,niobium,"or any other metal, or mixture, or'

alloy of these metals, upon which the infiltrant alloy may be based,provided the metal oralloy has a higher melting point than the'infiltrant.

The porous skeleton of refractory metal compound on which theprimary.coating is formed may'be produced in accordance with the method outlinedin copending application U .S'. Serial No. 442,564, filed July 12, 1954,now U.S..'Patent No. 2,752,666, inrthe names of Claus G. Goetzel andJohn -B. Adamec, also assigned to the present assignee. According tothis copending application, in producing refractory carbide skeletons orrefractory compound skeletons having intercommunicating pores,'hot orcold pressingmay be employed. It is preferred that these 7 materials,prior to pressing, be mixed with a binder metal in amounts up to 15% forexample such binder metals as iron, nickel, cobalt, etc. I p s I I-f thepowdermixture is cold-pressed into a porous 1 body, it-is given apre-s'intering treatment in a reducing atmosphere of ordinary orsub-atmospheric pressure below I 25.00 microns ofr'mercurycolumn,kpreferably at a te'r'n-' sintering treatment is not requiredprovided the hot pressing temperature is above the liquefaction,temperature of the cementing component. 1 After'the skeleton body isproduced'it may be machined to a size close torthe final specificationsif necessary, by cutting with cemented carbide tools, orby refractorywheel grinding, diamond chipping, orother methods commonly employedinthefabrication of'hard carbideproducts." In machining the body,

an over-size shrinkage allowance of about 2% to 10% is generally made,in order to compensate for the shrinkage which occurs in subsequentheating operations.

Final coating thickness ofthe infiltrated article may range fromone-thousandth toone-sixteenth .of an inch, preferably fromfive-thousandths to'thirty-thousandths,

' The thus preparedskeleton body is'thensubjected to a high temperaturesintering treatment in order to effect additional bonding of the carbideparticles'into 'a porous skeleton 'of sufficient strength to enable thebody to retain'its shape during subsequent infiltration treatment.

In carrying out thehigh temperature sintering operation,

it is preferred so 'sinterthe skeleton bodyat -a tempera- ,ture between,50 C. and 250 CL above the temperature;

used inthe subsequent infiltration operation in a technical vacuumcorresponding to a sub-atmospheric pressure rang ing froman initialpressure'of preferably notrmore than microns down to a final or,finishing pressure of 50 microns, of mercury and'preferably downto 10microns. The surrounding gas at such subatrnospheric pressure must benon-oxidizing to the body, i.e. .reducing or inert,'tol

borides, nitrides, silicid es, etc., of titanium, zirconium,

chromium, molybdenum,tungsten, vanadium, columbinm, tantalum, etc., andmixtures of two or more of these compounds. or the refractorycompoundirnay' also include.

such refractory oxidesas'oxi'des of aluminum, beryllium,

zirconium, thorium, magnesium,c erium etc: Theinvention ispreferablyapplicableto refractory metal carbides,

s particularly titanium carbide, or a carbide, based on titanium. Thus,titanium-base carbide may comprise up to about by volume of each of suchmetal carbides,

as silicon carbide, boron carbide, and up to about by volume each ofchromium carbide, columbium carbide, tungsten carbide, zirconiumcarbide, or hafnium carbide, the total amounts'of these carbidesgenerally not exceeding 25% by volume ofthe titanium-base carbide. Bytitanium-base carbide is meant a carbide comprising substantiallytitanium carbide.

The matrix-forming metals which may be employed in the metalliferoussystems referred to herein include the iron group metals iron, nickeland; cobalt, rr'iixturesthereof, and heat-resistant alloys based onthese metals,-i.e. heat resistant nickel-base, cobalt-base and ironbase.

Examples of nickel-base, matrix-forming alloys include; 80% nickel and20% chromium; 80% nickel, 14% chromium and 6% iron; chromium, 7% iron,1% niobium, 2.5% titanium, 0.7% aluminum and the balance nickel; 58%nickel, 15% chromium, 17% molybdenum, 5% tungsten and 5% iron; 95%nickel, 4.5% aluminum and 0.5% manganese, etc. 1

Examples of cobalt-base alloys which may. be employed as matrix-formingmetals include: 69% cobalt, 25 chromium, and 6% molybdenum; 65% cobalt,25 chromium, 6% tungsten, 2% nickel, 1% iron and other elements makingup the balance of 1%; 56% cobalt, 10% nickel, 26% chromium, and 7.5%tungsten, and some carbon; and 51.5% cobalt, 10% nickel, chromium, 15%tungsten, 2% iron, and 1.5% manganese, etc.

Some of the iron-base matrix-forming alloys include: 53% iron, nickel,16% chromium, and 6% molyb denum; 74% iron, 18%. chromium and 8% nickel;86% iron and 14% chromium; 82% iron and 18% chromium; 73% iron and 27%chromium, etc.

The matrix-forming infiltrant metal or alloy may contain up to about byweight of a metal selected from the group consisting of chromium,molybdenum and tungsten, the sum of the metals of said group preferablynot exceeding 40%, substantially the. balance being at least one irongroup metal selected from the group consisting of iron, cobalt andnickel, the sum of the iron group metals being'preferably at least about40% by weight of the matrix-forming alloy. If desired, the matrixfonningallo'y may also contain up to about 8% total of at least one metal fromthe group columbium, tantalum, and vanadium.

Alloys of the aforementioned types containing effective amounts ofso-called well-known strengthening or agehardening elements, such aszirconium, titanium, aluminum, etc., may also be employed inmatrix-forming metals or alloys.

'Metalliferous systems based on refractory metal compounds (e.g.titanium-base carbide) and matrix-forming metals, may be produced over awide range of compositions. In producing bodies by liquid phasesintering or by infiltration, the refractory metal compound may rangefrom about 40% to 80% by volume (preferably about 45% to 75%) and thematrix-forming metal range from about 60% to 20% by volume (preferablyabout 55% to 25% It will be appreciated that the present invention isalso applicable to the production of cladded products generally, forexample, to the production of cladded plates or other shapes ofrefractory carbide, or of other refractory compound material, wherein atleast one side is cladded. The invention may be utilized in theproduction of brazeable cladded surfaces for use as mold liners in brickmolds and other similar wear-resisting applications. Or, if desired, theinvention may be employed in producing laminated structures comprising aseries of alternate layers of a hard refractory compound andsubstantially ductile metal. In this case the laminated product would beproduced from a laminated composite skeleton comprising,

for example, sintered, porous, layers of titanium carbide alternatingwith sinteredporous layers of the primary metal coating. Uponinfiltration, the pores of the carbide and the alternate layers ofprimary coating would absorb the. infiltrant metal to form a solidlaminated product,

The expressions coat, coating, clad, cladding, etc.,'as employed hereinare meant to include thelayer of one material ontop of another, or alayer of, material between two other layers. The expression .compositeskeleton is meant to designate a porous skeleton body of refractorycompound material having adhering to it a primary metal coating.

While. the present invention has been described as a process forproducing coated or cladded composites, it will be appreciated it alsoprovides a combined infiltration and cladding mold assembly for carryingout saidprocess. Thus, an infiltration mold assembly isprovidedcomprising means for confining a powder pack of refractory oxidein which is supported snugly an infiltratable c0mposite skeleton body,the skeleton having on at least one surface thereof or between twosurfaces a foundation metallayer or primary metal coating ofpredetermined thickness.

In cross-section such a mold assembly may define at one side thereof aninner confining wall (efg. graphite) against which is packed refractoryoxide powder (e.g. zirconia or thoria) which in turn is packed snuglyagainst a composite'skeleton comprising a primary metal coating on asurface comprised substantially of a refractory metal compound (e.g.titanium carbide) which may or may not alternate with the primary metalcoating.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims. 4

We claim:

1. A method for simultaneously: infiltrating and coat ing a porousrefractory body which comprises producing a coherent porous skeletonofdesired shape comprising a high melting point refractory compoundmaterial adapted for infiltration with a matrix-forming metal, providingthe surface of said skeleton with a primary coating of metal ofpredetermined thickness, said metal having a melting point higher thanthe matrix-forming metal subsequently contained in the pores of saidskeleton, adequately supporting the;coated surface of said skeleton in apack of substantially inert refractory oxide material leaving a portionexposed for receiving infiltrant metal,

posed portion with said matrix-forming metal at a temperature below themelting point of the primary metal coating, and continuing saidinfiltration in said skeleton body whereby excess matrix-forming metalexfiltrates through the coated surface thereof and into the overlyingmetal coating and merges therewith by alloying.

2. A method for simultaneously infiltrating and coating a porousrefractory body which comprises producing a coherent porous skeleton ofdesired shape comprising a high melting point refractory compoundmaterial adapted for infiltration with a matrix-forming metal, providingthe surface of said skeleton with a substantially adherent primarycoating of metal in particulate form of predetermined thickness, saidmetal having a melting point at least 50 C. higher than thematrix-forming metal subsequently contained in the pores of saidskeleton, ardequately supporting the coated surface of said skeleton ina bed of substantially inert refractory oxide material leaving a portionexposed for receiving infiltrant metal, subjecting said coated skeletonto infiltration at the exposed portion with said matrix-forming metal ata temperature below the melting point of the primary metal coating,

11 and continuing said infiltrationwhereby excess matrixforming metalexfiltrates through the surface thereof and into the overlyingp'rimarymetallcoating and merges therewith.

3.- The method of claim 2wherein the primary metal coating inparticulate form is applied by metal spraying. 4. The method of claim'2wherein the primary metal coating in particulate form. is derived from asuspension of metal powder in a liquid binder solution. 1 i

5. The method of claim 4 wherein the metal powder suspension ranges inmesh size from minus 140 to plus 325. 1

6. A methodfor simultaneously infiltrating and coating a porousrefractory bodywhich comprises producing a coherent porous skeleton'ofdesired shape comprising a high melting point refractory compoundmaterial adapted for infiltration with a matrix-forming metal, providingthe surface of said skeleton with a primary coating of metal powder ofpredetermined thickness bonded together with a vaporizable binder, saidmetal having a melting point at least 50? :C. higher'than thematrix-forming metal subsequently contained in the pores of saidskeleton,'adequately supporting the surface of said coatedskeletonin abed of substantially inert refractory oxide powder leaving a portionexposed for receiving infiltrant metal, subjecting said coated. skeletonto heating to vaporize said binder, infiltrating said' coated skeletonwith said infiltrant metal, and continuing said infiltration wherebyexcess matrixforming metal exfiltrates through the surface of saidskeleton and into the overlying metal coating and merges and alloystherewith.

' 7 A method for simultaneously infiltrating and coating a porousrefractory body which comprises producing a coherent porous skeleton ofdesired shape comprising a high melting point refractory compoundmaterial adapted for infiltration with a matrix-forming metal, providingthe, surface pores of said skeleton with a heat curable resin, curingsaid resin in said pores, spraying said surface with a metal layer ofpredetermined thickness, said metal having a melting point at least 50C. higher than the matrix forming metal subsequently con-.

tained in the pores of said skeleton, adequately sup porting the surfaceofsaid coated skeleton 'in a bed. of substantially inert refractoryoxide powder leaving a portion exposed for receiving infiltrant metal,subjecting said coated skeleton to heating to vaporize said. binder,infiltratingsaid coated skeleton with said matrix-forming metal, andcontinuing said infiltration whereby excess matrix-forming metalexfiltrates through thesurface of said skeleton and into the overlyingmetal coating and merges and alloys therewith. 7 v

8. An infiltration and cladding mold assembly comprising a moldhaving'confined thereina powder pack substantially inert refractoryoxide material, a com.-

posite porous skeletonbody having ,a primary metal coat? ing ofpredeterminedfthickness .onfa't least one surface thereofand supportedby saidpowderpack 'at least adjacent said =coated surface, and meansassociated with one end of said skeleton for'receiving infiltrant metal.

9. An infiltration and cladding mold assembly comprising a mold havingconfined therein a powder pack of substantially inert refractory oxidematerial, a composite porous skeleton body having a primary metalcoating of predetermined thickness on at least one surface thereof andsupported by said powder pack at least adjacent said coated surface andmeans associated with one end of said skeleton for receiving infiltrantmetal, theprimary coat ing having a melting point higher than theinfiltrant metal.

10. An infiltration and cladding mold assembly comprising a mold havingconfined therein a powder packof substantially inert refractory. oxidematerial, a composite porous skeleton body having a porous primary metalcoating of predetermined thickness covering the surface thereof andsupported by said powder pack surrounding snugly said coated surface andmeans associated with one end of said skeleton for receiving infiltrantmetal, the primary metalrcoating having a melting point at least 50 C.higher than the infiltrant metal.

11. An infiltration and cladding mold assembly comprising a mold havingconfined therein a powder pack of substantially inert refractory oxidematerial, a composite porous skeleton body having a porous primary metalcoating of predetermined thickness covering the surface thereof andsupported ,by saidpowder pack surrounding snugly saidcoated surface, theprimary metal coating comprising particles of metal ranging in size'substantially from minus 140 mesh to 'plus 325 mesh, and meansassociated with one end of said skeleton'for receiving infiltrant metal,the primary-metal coating having a melting point at least C. higherthan'the infiltrant metal. i

References Cited in the file of this patent UNITED STATES PATENTS 72,119,989 Higgins June 7, 1938 2,325,553 Schleicher a July- 27, 19432,667,427 Nolte Jan. 26,1954 2,719,095 Scanlon Sept. 27, 1955 2,733,167Stookey Jan. 31, 1956 2,751,293 Haller June 19, 1956 2,768,099 HoyerOct. 23, 1956 2,769,611 Schwarzkopf Nov. 6, 1956 2,798,577 .La ForgeJuly 9, 1957 FOREIGN PATENTS 661,031 Great Britain Nov. 14, 1951

1. A METHOD FOR SIMULTANEOUSLY INFILTRATING AND COATING A POROUSREFRACTORY BODY WHICH COMPRISES PRODUCING A COHERENT POROUS SKELETON OFDESIRED SHAPE COMPRISING A HIGH MELTING POINT REFRACTORY COMPOUNDMATERIAL ADAPTED FOR INFILTRATION WITH A MATRIX-FORMING METAL, PROVIDINGTHE SURFACE OF SAID SKELETON WITH A PRIMARY COATING OF METAL OFPREDETERMINED THICKNESS, SAID METAL HAVING A MELTING POINT HIGHER THANTHE MATRIX-FORMING METAL SUBSEQUENTLY CONTAINED IN THE PORES OF SAIDSKELETON, ADEQUATELY SUPPORTING THE COATED SURFACE OF SAID SKELETON IN APACK OF SUBSTANTIALLY INERT REFRACTORY OXIDE MATERIAL LEAVING A PORTIONEXPOSED FOR RECEIVING INFILTRANT METAL, SUBJECTING SAID COATED SKELETONTO INFILTRATION AT THE EXPOSED PORTION WITH SAID MATRIX-FORMING METAL ATA TEMPERATURE BELOW THE MELTING POINT OF THE PRIMARY METAL COATING, ANDCONTINUING SAID INFILTRATION IN SAID SKELETON BODY WHEREBY EXCESSMATRIX-FORMING METAL EXFILTRATES THROUGH THE COATED SURFACE THEREOF ANDINTO THE OVERLYING METAL COATING AND MERGES THEREWITH BY ALLOYING.